This invention relates to a machining control method of a numerical control device (hereinafter referred to merely as "an NC", when applicable) for controlling a machine tool.
FIG. 1 shows the arrangement of an NC in four-axis control. In FIG. 1, reference numeral 1 designates a CRT (cathode ray tube) and keyboard assembly; 2, a control unit; 3, amplifier units; 4, electric motors; and 5, detectors.
FIG. 2 shows the arrangement of a four-axis lathe to which a machining control according to this invention is applicable. In FIG. 2, reference numeral 6 designates a first tool; 7, a first turret; 8, a second tool; 10, a workpiece moving along a Z-axis; and 11, a bushing for fixing the workpiece 10. The bushing 11 moves together with the workpiece 10 along the Z-axis The origin point of the machining program is designated as 0.
FIG. 3 is a block diagram showing a control system practiced by the control unit 2 and the amplifier units 3. In FIG. 3, reference numeral 12 designates an interpolating section for the first tool 6; 13, an interpolating section for the second tool 8; 14, an X-axis speed control section for the first tool 6; 15, a Z-axis speed control section for the first tool 6 (in practice, the workpiece being moved); 16, an X-axis speed control section for the second tool 8; 17, a Z-axis speed control section for the second tool 8; 18, an X-axis servo control section for the first tool 6; 19, a Z-axis servo control section (the Z-axis being of the workpiece 10) for the first tool 6, in which the direction of movement is reversed; 20, an X-axis servo control section for the second tool 8; and 21, a Z-axis servo control section for the second tool 8. Further in FIG. 3, reference characters fx1, fz1, fx2 and fz2 designate instruction speeds applied to the respective axes after interpolation; and Fx1, Fz1, Fx2 and Fz2, instruction speeds applied to the respective servo control sections.
First, the operator operates the keyboard 1 to input the machining programs which determine machining paths for the first and second tools 6 and 8, respectively. These machining programs are formed by referring to the machining program original point under the condition that the workpiece 10 is stationary; that is, it is machined with the tools 6 and 8 moving along the X-and Z-axis).
The control unit 2 forms tool moving instructions for the tools according to the machining programs thus inputted.
In response to the tool moving instruction for the first tool 6, the interpolating section 12 provides the instruction speeds fx1 and fz1 respectively for the X1-axis and the Z1-axis. The instruction speeds fx1 and fz1 thus provided are applied to the X-axis speed control 14 and the Z-axis speed control 15, respectively, which, in turn, applies the instruction speeds Fx1 and Fz1 to the servo control sections 18 and 19, respectively.
Similarly, in response to the tool moving instruction for the second tool 8, the interpolating section 13 provides the instruction speeds fx2 and fz2 respectively for the X2-axis and the Z2-axis. The instruction speeds fx2 and fz2 thus provided are applied to the X-axis speed control 16 and the Z-axis speed control 17, respectively, which in turn apply the instruction speed Fx2 and Fz2 to the servo control sections 20 and 21, respectively.
That is, after application of the tool moving instructions to the interpolating sections 12 and 13, the tools are controlled independently of each other.
The conventional NC control system is as described above. Therefore, in the case of the four-axis lathe in which, as shown in FIG. 2, the workpiece 10 is moved along the Z1-axis which is one of the control axes, while the workpiece being machined with the first tool 6 (i.e., the workpiece being moved), the machining program original point is also moving, and therefore the second tool 8 cannot be used until the workpiece 10 is returned to the machining program original point.